Sheet metal is usually protected from corrosion by being covered with lacquer. However, on the one hand it is difficult, to produce a faultless lacquer surface, and on the other hand the coating of lacquer is little resistant to scratching and impacts and is soon destroyed at weak spots by rust creeping under it. A much more durable protection is constituted by foils of synthetic material, which are cemented hot on the sheet metal, or layers of synthetic material, which are rolled as a pasty mass on the sheet metal. Such layers are resistant to impact, and can be produced in many different colours. They may, moreover, be made with patterns, texture and grains. Their use involves many advantages, but their economic treatment constitutes difficulties. They can be welded only, when the layer is removed from the areas to be welded. In order to restore a closed surface layer these areas have to be closed again. For this purpose no economically bearable methods have been available yet, so that coated sheet metal is used but little, in spite of its advantages. Since only the surfaces of the sheet metal are coated with layers, their edges remain uncoated, and so are likewise the cut edges formed when cutting the sheet metal to shape. In order to attain a perfect and durable protection from rusting, the edges of sheet metal have also to be covered.
Accordingly there exists the problem of protecting sheet metal, covered in various ways, on the blank or stripped areas thereof from corrosion, and to re-coat the same there, so that the work piece has on all sides a perfect rust-protecting layer. Moreover, machines and devices are to be developed which allow a quick and economic applying of the rust-protection, and which in particular can be fitted into a production line for mass production.